Wave guide structure



Oct. 22, 1946.l L -TONKS WAVE GUIDE STRUCTURE Filed Feb. 14, 1944 3Sheets-Sheet 1 Figi.

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OCL 22, 1946. TQNKS WAVE GUIDE STRUCTURE Filed Feb. 14, 1944 3Sheets-Sheet 2 Inventor` Lew Tonk; bg IIL-l His Attorney.

OCI; 22, 1946. L, TQNKS 2,409,913

IAVE GUIDE sTnUcTURE Filed Feb. 14, 1944 3 SheBtS-Sheet 3 Fig. X Figa Nl if' FigJO. Figli.

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Patented ct. 1946 WAVE GUIDE s'raUc'rUm; Lew: Tonks, Schenectady, N. Y.,signor-'tc Gem' eral York Electric Company. a corporation of NewApplication February 14, 1944, No. 522,241

l 1s claims.

My invention relates to ultra high frequency c systemsvand, inparticular. to apparatus for coupling an ultra high frequencygeneratorto a wave guide of the hollow pipe type. It is an object of myinvention to provide an improved electric discharge device to wave guidecoupling.

It is an object of my invention to provide a coupling arrangementbetween a magnetron generator and a wave guide of the hollow pipe typewhich is particularly'suited for the transmission of a large amount ofpower at a very short wave length.

same cut-oil frequency, said cut-off frequency being the same as that ofthe uniform wave guide fed by said tapered section. Moreover, thecrosssectional area at longitudinally positioned points is dimensionedto effect a gradual transition in impedance between the magnetrongenerator and the output wave guide.

The features of the invention desired t0 be protected herein are pointedout in the appended claims. The invention itself, together with itsfurther objects and advantages, may best be understood by the followingdescription taken in connection with the drawings in which Fig. 1 is avertical section of a magnetron device and a coupling arrangementsuitably embodying the invention; Fig. 2 is an end view serving toillustrate the magnetron structure employed in the device of Fig. l;Fig. 3 is an end view of the coupling arrangement of Fig. 1; Fig. 4 is alongitudinal section taken along the axis of one of the apertures of thecoupling arrangement; Fig. 5 is another view of the anode employed inthe magnetron of Fig. 1 showing the output arrangement; Fig. 6 is a viewof a uniform wave guide having a cross 2 section similar to that of thewave guide coupling; Fig. 'Lis a curve illustrating certaincharacteristics of the wave guide shown in Fig. 6; and Figs. 8-14illustrate other configurations of the cross section of the taperedcoupling arrangement of my invention.

Referring particularly to Fig. 1,' thereis shown an ultra high frequencygenerator I0 of the magnetron type which provides electromagnetic wavesof a predetermined frequency and mode to a dielectric wave guide I l ofthe hollow pipe type. 'I'he electromagnetic waves from the generator I0are transmitted to the waveguide II through a wave guide coupling I2which is dimensioned to aiford the same cut-oil' frequency toelectromagnetic waves at longitudinally positioned points, as well as toprovide a gradual transition in impedance between the magnetron outputand the wave guide I While my improved coupling arrangement may beemployed with any suitable ultra high frequency generator, one suitabledevice is shown in Fig. 1 as the magnetron III which comprises anelongated cylindrical container. the lateral wall structure of which isprovided by a single metallic tube I3 consisting of ferromagneticmaterial, such as cold rolled steel or the like. Opposite ends of thecontainer are similar in construction and are closed by flanged membersI4 which are welded or otherwise hermetically joined to the innersurface of the part I'Il. Within the container and approximately at itscentral region, there is provided an anode structure I5 shown in planview in Fig. 2. This anode structure comprises a circular metallicmember which has a relatively large central opening i6 and a series of vsmaller openings Il arranged symmetrically about the central opening,and the central opening i8 is joined to the openings II by means oflaterally extending slotsl. Alternate ones of the metallicv walls oranode posts between the slots I8 are electrically connected together bymeans of conductive `straps I9.

Within the opening I6 of the anode structure, as shown in Fig. l, thereis provided anindirectly heated cathode comprising a sleeve 2i of nickelcor. other suitable material having flanges 22 spun up at itsextremities. 'Ihis sleeve, which may be coated externally ,with asuitable activating material such as barium oxide. contains a la- 3 Ymentary heater 2l by which it may be maintained at an emissivetemperature. Que end of the cathode sleeve is closed by a metal disk 25,while an apertured disk 26 partially closes its other extremity.

In the operation of the device. a space charge is assumed to bedeveloped in the space between the cathode sleeve 2l and the surroundinganode structure by the application of a suitable potential impressedbetween the cathode lead-in wire 28 and the container I to which theanode structure is directly conductively connected. The electrons whichcompose this space charge :are given a spiral or orbital motion by amagnetic field produced by means to be described hereinaiter, and theirresultant gyrations about the cathode produce excitation of the anodestructure at its resonant frequency. The functioning oi the anodestructure inthe latter connection may be explained from one point ofView by consid ering that it 'ls made up of a plurality of mutuallycoupled resonant units, in each of which induct-l ance is provided bythe wall surface bounding one of the circular openings l'l andcapacitance is provided by the opposing surfaces of one oi the slotsiii. Taking this viewpoint, it is seen that the operating frequency isdetermined in a large measure by the dimensions of the openings i1.

For the purpose of providing a magnetic field of suicient intensity topermit the apparatus to function in its intended fashion, there areprovided within the container I3 tapered magnetic pole pieces dit and 3iwhich are directed axially of the container and which extend in closeproximity to the upper and lower surfaces of the anode structure i5.These pole pieces are permanently magnetized in such sense that thenorth pole of one faces the south 'pole of the other. in order to assurethe existence of a magnetic held of the required intensity, the polepieces at, 3i are constituted of a magnetizable substance having a highcoercive force and a high energy factor. one material which may 4be usedin this connection is that known as Alnico, a name designating aparticular class of alloys of aluminum, nickel, and cobalt. .As analternative structure, instead of using permanent magnets for polepieces 30, 3i, soft iron pole pieces may be used and may be magnetizedby means of an external winding (not shown).

In order to provide a low reluctance connection between the basicextremities of the respective pole pieces and the lateral wall of thecontainer I3, the pole pieces may be respectively seated upon relativelythick disk-like members 33 consisting of ferromagnetic material, such assteel, and may be secured to these members by means of a clamping ring34 slipped over the pole pieces andwelded to themembers 33. The basemember 33 is of such diameter as to lit snugly within the tubularcontainer I3 so as to provide a low reluctance connection with thatpartc and is welded to the associated closure member I4.

Accurate spacing of the pole pieces 30, 3i with reference to the anodestructure I5 may be obtained by the use vof spacing rings 36 interposedbetween anode structure i5 and the sur-v face ci an apertured disk 31.

The Vwave, guide li is illustrated as a hollow pipe having a rectangularcross section and defined by conductive .side walls dii and conductivetop and bottom walls 4I, 42. It is well known that ultra high frequencyelectromagnetic waves may be propagated dielectrically through such ahollow-pipe type wave guide Where the frequencyof the eacitingelectromagnetic waves is' greater than Aa critical minimum frequencyguides. These waves have been generally -indicated heretofore as beingof the TE and TM types. The TM type waves have both a longivtudinal andtransverse component of electric ileld but only a transverse componentof magnetic held, whereas the TE type waves have both a longitudinal andtransverse component oi.' magnetic field but only atransverse componentof electric ileld. Electromagnetic waves of this type may be extractedfrom a magnetron, such as the' -illustrated magnetron ld. Although myinvention is applicable to systems for transmitting a greater variety ofwaves, in describing my invention hereinafter reference will be madeparticularly to the TEm type of wave.

In order to provide means for directly coupling electromagnetic wavesgenerated in the magnetron ill to the wave guide il the transitioncoupling section l2 is interposed between the wave guide il and themagnetron I0. The tapered transition section I2, as seen in Fig. 3,comprises a metallic member 44 whose cross section has two substantiallycircular aperturer 45, therein connected together by a rectangular slot4l. The size of the holes 45, 56 and of the slot 41 increases uniformlyfrom the end of the member i2 connected to the magnetron to its point ofconnection with the wave guide II.

The transition section- I2 may be constructed by forming twosemi-circles at the wave guide end of metallic member 44, eachsemi-circle being tangent substantially to three sides of therectangular wave guide II. The two semi-circles are connected togetherby two .straight edges 49, 5U, as shown in Fig. 4. At its opposite endthe member 44 isvr provided with an oriiice comprising two symmetricallypositioned holes 5I, l2 joined together by a rectangular slot 53, asshown in Fig. 3. The member M may then be bored with two conical holeswhich nt the large semi-circles at the Wave guide end of the member andthe circles 5I, 52 at the magnetron end of vthe member. The partitionbetween the hollow cones is then out away so that every cross section isof dumb-bell shape and of such proportions that a uniformguide of thatsame cross section would have a cut-oh' frequency substantially equal tothe wave guide cut-oft frequency. At the same time, the coupling memberI2 eiects a gradual change in impedance between the impedance at itsmagnetron end, whereits value is such that it provides optimum couplingAwith the cavity resonator of the magnetron, and the impedance at itswave guide end, where its 'value matches that of the wave guide II.V

For purposes of transmitting electromagnetic energy from the magnetroninto' the coupling section i2, the anode I5 is flattened at one point toprovide a at wall 55,l as shown in Fig. 5, against which the left-handend of the cou-V pling section i2 abuts. The at wall 55 of the anode isprovided with an output oriiice of dumb-bell shape which comprises twocircular openings 56, El equal in diameter to the openings 5i, 52 ofcoupling l2 and connected by a rectangular slot 58 which coincides withthe slot 53 of coupling member l2. The cylindrical tank I3 may beprovided with an aperture overlying the wall 55 of anode Il'throughwhich a constricted portion 66 of coupling member I2 projects. Thecoupling member l2 may be secured to tank I3 of the magnetron in anysuitable el-cobalt alloy. to facilitate sealing of the window i thereto.Wall 62 is interposed between the abut-- ting end's of coupling memberI2 and wave guide I I, being brazed or welded to member I2. A conductivestrap 63 welded or brazed to both members II and I2 strengthens thejoint.-

into a corresponding shoulder in wall 62 on the high pressure sidethereof, to strengthen the glass to metal seal. After the window 6I issealed in Iplace. the magnetron and the coupling unit I2v may beevacuated through an exhaust tubulation 69 connected to the bottom ofthe magnetron structure.

The operation of -thewave guide coupling unit I2, as well 'as itsdimensioning, may be better understood from the following description ofthe propagation characteristics of the dumb-bell cross section waveguide, which. in tapered form, constitutes the coupling unit. To assistin this explanation, reference is made to Fig. 6 of the drawing whereinthe circular openings 5I, 52 are shown as having a diameter d. Thedistance between the centers of the circular openings 5I, 52 isdesignated as the dimension l. The length of the slot 53 is shown asequal to 2b and the height of this slot as having a value t. 'I'he anglesubtended by half of the gap 53 at the center of one of the holes 5I, 52is equal to a.

I'he curves in Fig. 7 have been derived by the suitable application ofMaxwells equations to the propagation space of the wave guide shown inFig. 6. These curves give the dimensions of cross sections which producea cut-ofi wave length of 10.0 centimeters. 'For example, a cross sectionin which t=.018 inch, l=0.5 inch, and d=0.2 inch, has its cut-oil' at 10centimeters, because for it d/l=0.4, and following the d/l=0.4 line 70on Fig. 7 to its intersection with the l=0.50 curve. it is seen thatthat intersection lies also on the :.018 inch line.

Certain approximations have to be made in the mathematical theoryleading to Fig. 7, with the consequence that the curves aresubstantially valid over a limited region which is defined by the dashedcurves labelled l=0.5 radian and t=l-d. It is well known that to apply aset of curves, such as those of Fig. 7, to a structure having a cut-ofiwave length of l centimeters, diierent from 10 centimeters. it is onlynecessary to multiply the actual dimensions by 10/7l thereby obtainingscaled values to which Fig. 7 is applicable.

By way of illustrating the procedure of obtaining from Fig. 7 thedimensions for a tapered wave guide coupling section, consider an actualexample in which the wave guide I1, of Fig. 1 is 1.44

vinches x 2.84 inches, inside dimensions, the tapered section I2 is 4inches long from magnetron block I5 to wave guide II, and the oriilce56, 51, 56 at the small end is approximately 1 inch long over all.

The 2.84 inch dimension of the wave guide immediately xes the cut-oilwavelength A@ as 14.5

Window 6| is provided with a shoulder yportion 6l, which iltscentimeters. If we assume a given slot thickness for slot ,58 and avalue for the dimension l,

the curves of Fig. 7 enable us to calculate thedimension d. Assumptionof a sequence of values for t and l enables us to reach the followingset of values which are consistent with Fig. 7 and which are primed todistinguish them from actual dimensions: I

When multiplied by the ratio 14.5/10, the desired values are given as .1

l1= .725 di 276 0174 li-l-di =1. 001

Sinceithe circular arcs at the large and small ends are joined byconical surfaces, it follows that for any cross-section a fractionaldistance .f (shown in Fig. 4) from small to large end It is thenpossible to construct the following table:

The values of f in horizontal row 1 are chosen conveniently andarbitrarily. Rows 2 and 3 are calculated by Equations 1 and 2. Row 4follows from rows 2 and 3. Row 5 is obtained by multiplying row.3 by theratio explained. Row 6 is taken from Fig. 7 using rows 4 and 5, exceptin vertical column 8 which applies to the rectangular wave guide. Row 7is row 6 multiplied by 14.5/ 10.

Thus the dimensions of the coupling section are complete up to half thedistance from the small or magnetron end to the wave guide end. It isseen, however, that Fig. 7 does notapply beyond l=0.5 so that anotherconsideration has to -be used. The 4curve of t against f in Fig. 4 iscontinued as a smooth curve to t=1.44 at; f=1, that is, at the wave'guide junction, as indicated in Fig. 4.

In connection with the foregoing illustration,v

the wave` length or the electromagnetic wave 10/14.5 as previouslysection, that is. the cut-oi! wave length of a uniform wave guide havingthis particular cross section, must be greater than the wave length otthe wave being propagated. Another important advantage of the couplingarrangement is that the gradually tapered section provides anessentially smooth transition in impedance so that the coupling sectionis substantially reilectionless at all points beyond approximately 11sof a wave length from the point 'of connection to the ultra highfrequency generator.

While in the illustrations and discussion thus far the cross section ofthe coupling member I2 has beenI described as being substantiallydumbbell in shape, the cross section of the section I2 need not belimited to this particular shape and 8 What I `claim. as new and desireto secure by Letters Patent of the United States is:

1. A wave guide of the hollow pipe type defined by a block of metalprovided with a tapered longil tudinal opening, every cross section of,said opening taken at .longitudinally positioned points thereofcomprising a narrowed central portionv and being dimensioned so that aluniform wave guide of said cross section would ailord the same cut-oi!frequency to electromagnetic waves.

2. A couplingl device for an ultra high irequency transmission systemcomprising a conductive member defining'therein a tapered longitudinalopening the cross-sectional arca of which at longitudinal pointscomprises a'. narrowed central portion and is dimensioned to have apredetermined variation in impedance along Ithe any other suitable crosssection may be employed, l

the apertures in the member tapering from the point of connection to theultra high frequency device to the end connected to the wave guide I I..

In Figs. `8l2, there are shown other coniiguras tions of cross sectionsfor the coupling member I2, all of which employ a pair of apertures 80,8I

, connected by a slot 82. Each of the apertures and the slot are taperedbetween the two ends of the coupling member I2. Fig. l1, for example,shows a cross section which is rectangular in form and Fig. 12, onewhich is octagonal in form. t

In Fig. 13, there is shown a cross section for the couplingmember I2 inwhich the two tapered apertures 80, Stare not of the same size so thatthe symmetry oi' form illustrated in the preceding cross section viewsof the coupling member I2 is not present in this particular form oi'coupling member. A similar asymmetrical condition may ibe employed incoupling members using circular apertures, as well as members usingrectangular apertures, as in Fig 13. In Fig. 14. the slot connecting thetapered apertures 80, SI is of a sinuous type and consists of a pair ofparallel passages 33, 84 and a connecting passage 85. Congurations inthe cross section of a coupling unit of this type are especiallydesirable where the cut-off frequency oi the wave being propagated' isrelatively low so that extremely large wave guide sections would :berequired.

It is apparent, moreover, that, while the wave guide II is illustratedas of the rectangular type, 'the coupling member I 2 may-be employed toconnect the output 'of an ultra high frequency device to a wave guide ofany given configuration, the criteria'being that the cut-off wave lengthat every cross section must be greater than the wave v length of theelectromagnetic wave being propagated and that a gradual transitionimpedance be effected between the two ends ,of the couplim unit toeffect a match with the impedanceof the wave guide connected thereto.Such a coupling is particularly suited for the transmission of largeamounts of energy of relatively short wave length. r

While I have shown a particular embodiment of my invention, it will ofcourse be understood that I do not wish to be limited thereto sincevarious modifications may be made, and I contemplate fby the appendedclaims to cover any such modications as fall within the true spirit and-scope of my invention.

longitudinal axis.

3. A coupling 'device for use in an ultra high frequency transmissionsystem comprising a conductive member having a tapered longitudinalopening extending therethrough the cross section of which at one end isdeilned by an elongated central opening terminated at each end in anenlarged opening the last mentioned open- -ings progressivelyyincreasing in cross-sectional area in the longitudinal direction.

4. A dielectric wave guide of the hollow-pipe type comprising a block ofmetal having tlierein a tapered longitudinal opening the cross sectionalarea of which at one end includes a central elongated slot terminatedateach end thereof in` an enlarged circular opening, the last mentionedopenings progressively increasing in cross secltional area in thelongitudinal direction.

5. In combination, a dielectric wave guide of` the hollow-pipe typecomprising a conductive member of'rectangular cross sectionan ultra highfrequency generator. comprising a cavity resonator, and means. forcoupling said Wave guide and said cavity resonator comprising aconductive member having therein a tapered longitudinal opening thecross sectional area of whichl at longitudinal points comprises anarrowed central portion and is dimensioned to effect a gradualtransition in impedance. 'f

6. In combination, a waveguide of the hollow pipe type, an Yultra, highfrequency generator comprising'a cavity resonator, and means forcoupling said wave guide and said cavity resonator comprising aconductive member having a length greater than 1x5 of afree space wavelength of area of which at longitudinal pointsvcomprises,

onator, said member being provided with an aperture through which highfrequency',y energy may be extracted, a dielectric wave guide of thehollow pipe type, and coupling means for `connecting said generator tosaid Wave guide comprising a metallic vmember Ahaving' therein a taperedlongitudinal opening the cross sectional a constricted central portionand is dimensioned to have a substantially uniformcut-off`characteristic and having at one end adjacent said generator ageometry similar to said aperture.

8. In combination, an ultra high frequency magnetron of thespace'resonant type comprism ing a plurality of electrodes including ananode structure for defining a. cavity resonator, said anode structurebeing provided with an aperture comprising a central slot terminated atthe ends in circular openings, a dielectric wave guide of the hollowpipe type having a rectangular cross section, and coupling means betweensaid anode structure and said wave guide comprising a conductive memberhaving a tapered longitudinal opening the cross sectional area of whichis dimensioned at one end adjacent said anode structure for optimumcoupling to said cavity resonator and dimensioned at the other end tomatch the impedance of said guide.

9. In combination, an ultra high frequency magnetron of the spaceresonant type comprising a plurality of electrodes including anuanodestructure for defining a cavity resonator, said anode structure beingprovided with an aperture, a dielectric wave guide of the hollow pipetype, and coupling means between said anode structure and said guidecomprising a conductive member having a tapered longitudinal opening thecross sectional area of which comprises a narrowed central portion andis dimensioned to have a transitional impedance which provides optimumcoupling to said cavity resonator and impedance matching with saidguide.

10. In combination, an ultra high frequency generator of the spaceresonant type including a structure for deiining a, cavity resonator,said structure being provided with an aperture through which the energyof said cavity resonator may be extracted, a, dielectric Wave guide ofthe hollow pipe type, and coupling means between said structure and saidwave guide comprising a conductive member having a tapered longitudinalopening the cross sectional area of which comprises a narrowed centralportion and is dimensioned to aord a transitional impedance whichprovides optimum coupling to said cavity resonator and impedancematching with said wave guide.

11. A dielectric wave guide of the hollow pipe type defined by a blockof metal having a longitudinal opening comprising a pair of longitudinaltapered openings joined by an intermediate slot, the separation ofopposing faces of said slot increasing with the cross sectional area ofsaid tapered opening.

12. A dielectric wave guide of the hollow pipe type defined by a blockof metal having a longitudinal opening comprising a pair of longitudinalconical openings joined by an intermediate slot the separation ofopposing faces of which increases in accordance with the cross sectionalarea of said conical openings.

13. A discharge device for an ultra high frequency transmission systemcomprising a conductive member deiining therein a tapered longitudinalopening comprising a pair of longitudinal conical openings joined by anintermediate slot the separation of opposing faces of which increases inaccordance with the longitudinal cross sectional area of the conicalopenings to produce at one end a substantially rectangular opening forconnection to a dielectric wave guide of the hollow pipe type.

LEWI TONKS.

